A 20.0 kg rock is dropped and hits the ground at a speed of 90.0 m/s. What is the rock's gravitational potential energy before it was dropped?

1 Answer
Mar 14, 2018

GPE = 81000J or 81kJ

Explanation:

ground level = KE_0 , GPE_0
*before it was dropped = KE_h, GPE_h

GPE_h + KE_h = GPE_0 + KE_0

KE_h = 0 and GPH_0 = 0

So

GPE_h = KE_0

GPE_h = 1/2m(v)^2

GPE_h = 1/2 * 20 * (90)^2

GPE_h = 81000J = 81kJ